In production technology in the field of integrated circuit in an electronic industries, demand for high integration and speed-up is increasing. With respect to silicon ULSI, especially logic ULSI, rather than performance by miniaturization of MOSFET, performance of wiring connecting those has been problematic. Namely, reduction in wiring resistance and reduction in capacitance between wirings and in interlayer capacitance are required in order to solve the problem in wiring delay due to multilayer interconnects.
Accordingly, at present, instead of aluminum wiring used for the most part of the in integrated circuit, introduction of copper wiring having a lower electric resistance and migration resistance is essential, and a process of conducting copper plating after seed formation by sputtering or chemical vapor deposition (hereinafter abbreviated as CVD) method has been used practically.
There are various proposals as a low dielectric constant interlayer insulating film material. Heretofore as the inorganic system, silicon dioxide (SiO2), silicon nitride and a phosphosilicate glass have been used, and as the organic system a polyimide has been used. However, recently, with a purpose of obtaining a more homogenous interlayer insulating film, there are the proposal of previously hydrolyzing, that is, polycondensing, a tetraethoxysilane monomer to obtain SiO2, and using as a coating material called inorganic Spin on Glass (inorganic SOG), and the proposal of using a polysiloxane obtained by polycondensing an organic alkoxysilane monomer, as an organic SOG.
Further, as a method of forming the insulating film, there are the following two methods. An application method of a coating method of coating an insulating film polymer solution with a spin coat or the like to form a film, and a CVD method of mainly plasma polymerizing in a plasma enhanced chemical vapor deposition (PECVD) equipment to form a film.
As the proposal of the PECVD method, for example, Patent Document 1 proposes a method of forming a trimethylsilane oxide thin film from trimethylsilane and oxygen by the PECVD method, and Patent Document 2 proposes a method of forming an alkylsilane oxide thin film from an alkoxysilane having a straight-chain alkyl such as methyl, ethyl and n-propyl, an alkynyl such as vinyl, phenyl, and an aryl group by the PECVD method. Those insulating films formed with the conventional PECVD method materials have good adhesion to a barrier metal and a copper wiring material which is a wiring material, whereas there were the cases that uniformity of a film becomes problem and film formation rate and dielectric constant are insufficient.
As the proposal of PECVD using a cyclic siloxane, Patent Document 3 proposes a method of using tetramethylcyclotetrasiloxane, and Patent Document 4 proposes a method of using tetraalkylcyclotetrasiloxane, tetraminocyclotetrasiloxane, octaalkylcyclotetrasiloxane or octaminocyclotetrasiloxane. Those methods intend to lower dielectric constant by using a cyclic siloxane as a raw material compound to form pores in a thin film formed, while maintaining its cyclic structure in the thin film formed. However, according to the present inventors' finding, when a film is formed by PECVD using those substituted cyclic siloxanes, a thin film having dielectric constant of less than 2.7 is not obtained. This is considered due to that a cyclic structure of its cyclic siloxane compound is easily disintegrated in plasma to form a chain structure, and thus does not contribute to make a porous thin film.
Further, Patent Document 5 proposes a six-membered cyclic siloxane such as hexamethylcyclotrisiloxane and 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane, and Patent Document 6 proposes to copolymerize a bisbenzocyclobutene-substituted disiloxane compound and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane as an eight-membered cyclic siloxane under a plasma condition. However, according to the present inventors' finding, a thin film having dielectric constant of less than 2.5 is not obtained by a method of using vinyl- and/or methyl-substituted cyclic siloxane as proposed by those.
Patent Document 7 and Patent Document 8 propose a film formation method of a low dielectric constant thin film by PECVD method using a porogene. The former proposes a method of lowering dielectric constant by feeding triethoxysilane, diethoxymethylsilane and α-terpinene as a porogene in PECVD equipment chamber, forming PECVD film, and annealing at a temperature of 400° C. or higher to vaporize a component derived from α-terpinene in a thin film, thereby making the thin film porous. The latter proposes a method of lowering dielectric constant by supplying cyclo-1,3,5,7-tetrasilylene-2,6-dioxy-4,8-dimethylene, vinylfuryl ether as porogene, and nitrous oxide as an oxidizing agent in PECVD equipment chamber, forming PECVD film, annealing at a temperature of 400° C. or higher, and vaporizing a component derived from vinylfuryl ether in a thin film, thereby making the thin film porous. Those methods can expect to lower dielectric constant by pore formation. However, the component derived from porogene is removed from the inside of the thin film once formed, into the outside thereof by a post-treatment. Therefore, there are the problems that matrix of the thin film is disintegrated, a composition in the inside of the film becomes heterogenous, mechanical strength such as hardness and Young modulus deteriorates, pores formed become a continuous open pore, and diffusion of a metal component into a film is not prevented.
On the other hand, as the proposal of coating type, although uniformity of a film is good, three steps of coating, solvent removal and heat treatment are necessary, and this is economically disadvantageous than CVD material. Further, there are many cases that adhesion to a barrier metal and a copper wiring material as a wiring material, and uniform coating of a coating liquid to a miniaturized substrate structure become the problem.
Further, in the coating type material, a method of forming a porous material in order to form Ultra Low-k material having dielectric constant of 2.5 or lower, and further 2.0 or lower is proposed. There are a method of forming pores by dispersing organic component fine particles which are easily thermally decomposed, in a matrix of an organic or inorganic material, and heat treating; a method of forming SiO2 ultrafine particle thin film by evaporating silicon and oxygen in a gas to deposit SiO2 ultrafine particles formed; and the like. However, those pore forming methods are effective to lower dielectric constant, but there were the cases that mechanical property deteriorates, Chemical Mechanical Polishing (CMP) becomes difficult, and water adsorption gives rises to heighten of a dielectric constant and wiring corrosion due to adsorption of moisture.
Therefore, the market further requires materials having good balance satisfying all of the requirements of low dielectric constant, sufficient mechanical strength, adhesion to a barrier metal, prevention of copper diffusion, plasma ashing resistance, moisture resistance and the like. As a method of satisfying those requirements with good balance in a certain degree, a material is proposed which has intermediate properties between an organic polymer and an inorganic polymer by increasing carbon proportion of organic substituents to silane in an organic silane material. For example, Patent Document 9 proposes a method of obtaining an interlayer insulating film having dielectric constant of 2.4 or less using a coating solution obtained by hydrolytically polycondensing a silicon compound having an adamantyl group in the presence of an acidic aqueous solution by a sol-gel method, without forming pores. However, this material is a coating type material, and still has the problem of the film forming method by a coating type as described above.    Patent Document 1: JP-A-2002-110670    Patent Document 2: JP-A-11-288931    Patent Document 3: Japanese Patent No 2067801    Patent Document 4: JP-A-5-279856    Patent Document 5: WO 03/019645 pamphlet    Patent Document 6: JP-A-2004-47873    Patent Document 7: JP-A-2005-19980    Patent Document 8: JP-A-2001-298023    Patent Document 9: JP-A-2000-302791